HONG KONG — A boat packed with revelers on a long holiday weekend collided with a ferry and sank off Hong Kong, killing at least 36 people and injuring dozens, authorities said.

The boat was carrying utility company workers and their families to famed Victoria Harbour to watch a fireworks display in celebration of China’s National Day and mid-autumn festival. The two vessels collided Monday night near Lamma Island off the southwestern coast of Hong Kong Island.

The government said 36 bodies had been recovered as of Tuesday morning and the search was continuing. More than 100 people were rescued and sent to hospitals, and nine had serious or critical injuries, the government’s statement said.

Such large-scale accidents are rare for Hong Kong, a semiautonomous enclave off mainland China that has one of Asia’s most advanced infrastructures and economies with first-rate public services.

“All of Hong Kong’s emergency forces are focused here,” said Hong Kong’s leader, Chief Executive Leung Chun-ying. “Wide-ranging rescue work is being carried out on in the sea, land and in the air.” Leung said he didn’t know what caused the collision but promised a thorough investigation.

After daybreak, the boat was half submerged with its bow pointing almost straight up. A barge was tied alongside it, apparently to stabilize the sunken boat and keep it from tipping further.

The government statement said low visibility and obstacles on the boat were making rescue efforts difficult. It said the possibility people were still in the vessel or missing could not be ruled out, though it did not give numbers.

“There was a boat that came in close and crashed,” said Yuen Sui-see, director of operations at Power Assets Holdings Ltd., which was using the vessel to take staff on the outing. “After the crash, the other boat continued away, it didn’t stop.” He denied the vessel was overloaded, saying it was carrying 121 passengers and three crew but had capacity for more than 200 passengers.

Local news reports said the boat was hit by a ferry operated by the Hong Kong and Kowloon Ferry company on a regularly scheduled service. RTHK said the captain of the other ship, which was slightly damaged but able to return to port, was afraid to stop in case it sank, too.

Survivors said the boat started sinking rapidly after the collision. One woman told local television that she swallowed a lot of water as she swam back to shore. Another man said he didn’t know where his children were. Neither gave their names.

Lamma is the third-biggest island in Hong Kong and near one of the coastal Chinese city’s busiest shipping lanes. The island is home to about 6,000 people, including many of the former British colony’s expatriate workers.